I don't like Caballes. I think it leads to a dark future. Stevens wrote: “Critical to that [Kyllo] decision was the fact that the device was capable of detecting lawful activity."
So, based on your analysis that the search only occurs when it provides a result to a human, and the holding in Caballes that any result provided to a human that could only pertain to unlawful activity cannot be called a search, it seems this is not a search (for 4th amendment purposes).
Edge cases about hash collisions would likely be dismissed as easily as edge cases about the police misinterpreting the dog or the dog barking at the wrong time.
So, the bottom line becomes, any technology that we can develop to collect information about crimes is A-OK so long as it never provides any information to a human being unless an actual crime has been committed.
Let your fantasies about orwellian high-tech distopias fly! Hash checks of internet communications at ISP's? Check! Compulsary installation of face recognition cameras in all private buildings? No problem!
Artificial intelligences that read email correspondence or analyze search engine queries for patterns indicating criminal behavior? Well, they would have to be highly accurate, which is a bit far fetched by present technological standards, but if they were, then that might be alright as well...
Eventually in the distant future, you reach a point that has been mentioned by previous posters, where you've replaced your human police officers with robots... These robots are artificially intelligent and never report the results of their investigations to humans unless a crime has been committed.
Under this analysis I cannot see how the Constitution would prohibit these robots from doing all of the tyrannical things that the 4th amendment was intended to prevent the police from doing, and I don't see how this state of affairs would be materially different from not having any 4th amendment at all.
Therefore, if the 4th amendment is to have any meaning at all, there must be some reason that this kind of automated search is not reasonable.
Scalia offered the following in reference to Caballes: "This is not a new technology. This is a dog." I find that explanation extremely unsatisfying.